Systems and methods using interferometric optical modulators and diffusers

ABSTRACT

Various embodiments include interferometric optical modulators comprising a substrate layer having a thickness between about 0.1 mm to about 0.45 mm thick and a method for manufacturing the same. The interferometric modulator can be integrated together with a diffuser in a display device. The thin substrate permits use of a thicker diffuser. The thinner substrate may increase resolution and reduce overall thickness of the inteferometric modulator. The thicker diffuser may provide increased diffusion and durability.

PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/607,932, filed Oct. 28, 2009, entitled “SYSTEMS AND METHODS USINGINTERFEROMETRIC OPTICAL MODULATORS AND DIFFUSERS,” which is acontinuation of U.S. patent application Ser. No. 11/209,143, filed Aug.22, 2005, entitled “SYSTEMS AND METHODS USING INTERFEROMETRIC OPTICALMODULATORS AND DIFFUSERS,” now U.S. Pat. No. 7,710,636, which claimspriority to U.S. Provisional Application No. 60/613,568, entitled“SYSTEM AND METHOD FOR INTERFEROMETRIC OPTICAL MODULATOR AND DIFFUSER,”filed Sep. 27, 2004; all of the above applications are herebyincorporated by reference herein in their entirety.

BACKGROUND

1. Field of the Invention

The field of the invention relates to microelectromechanical systems(MEMS).

2. Description of the Related Technology

Microelectromechanical systems (MEMS) include micro mechanical elements,actuators, and electronics. Micromechanical elements may be createdusing deposition, etching, and or other micromachining processes thatetch away parts of substrates and/or deposited material layers or thatadd layers to form electrical and electromechanical devices. One type ofMEMS device is called an interferometric modulator. As used herein, theterm interferometric modulator or interferometric light modulator refersto a device that selectively absorbs and/or reflects light using theprinciples of optical interference. In certain embodiments, aninterferometric modulator may comprise a pair of conductive plates, oneor both of which may be transparent and/or reflective in whole or partand capable of relative motion upon application of an appropriateelectrical signal. In a particular embodiment, one plate may comprise astationary layer deposited on a substrate and the other plate maycomprise a metallic membrane separated from the stationary layer by anair gap. As described herein in more detail, the position of one platein relation to another can change the optical interference of lightincident on the interferometric modulator. Such devices have a widerange of applications, and it would be beneficial in the art to utilizeand/or modify the characteristics of these types of devices so thattheir features can be exploited in improving existing products andcreating new products that have not yet been developed.

SUMMARY OF CERTAIN EMBODIMENTS

The system, method, and devices of the invention each have severalaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope of this invention, its moreprominent features will now be discussed briefly. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description of Certain Embodiments” one will understand howthe features of this invention provide advantages over other displaydevices.

One embodiment includes a display comprising a plurality of displayelements, each of the display elements comprising a movable reflector, apartial reflector positioned at a distance from the movable reflectorthereby forming an optical resonator cavity, said movable reflector andsaid partial reflector separated by a gap, a diffuser portion disposedforward the movable and partial reflectors, and an electrode configuredto cause said movable reflector to move with respect to said partialreflector and to alter said optical resonator cavity, wherein (i) theplurality of display elements has a reflectivity at a viewing angle ofabout 45° that is greater than about 75% of the reflectivity of theplurality of display elements when viewed from normal and (ii) thediffuser portions are disposed sufficiently close to the partiallyreflective layers such that the plurality of display elements achieve acontrast of greater than about 5 to 1 while using a displayed testpattern of alternating white and black lines of a spatial period of lessthan about 0.45 millimeter.

Another embodiment has a display comprising a plurality of displayelements, each of the display elements comprising means for spatiallymodulating light by interferometrically modulating reflectivity, saidspatial modulating means having a maximum resolution less than about0.45 millimeter, and means for diffusing said light, wherein (i) in onestate, said plurality of display element have a reflectivity at aviewing angle of about 45° that is greater than about 75% of thereflectivity of the display when viewed from normal, and (ii) saidplurality of display elements produce a display contrast greater thanabout 5 to 1 for a test pattern comprising alternating white and blacklines with said maximum resolution of said spatial modulating means.

Still another embodiment has a method of manufacturing a displaycomprising a plurality of display elements, said method comprisingforming a movable reflector, forming a partial reflector positioned at adistance from the movable reflector thereby forming an optical resonatorcavity, said movable reflector and said partial reflector separated by agap such that said movable reflector can move toward said partialreflector to modulate said optical resonator cavity, forming a diffuserdisposed within about 0.45 millimeter or less of the partiallyreflective layer, and forming an electrode configured to cause saidmovable reflector to move with respect to said partial reflector.

Yet another embodiment has a display comprising a plurality of displayelements, each of the display elements comprising a movable reflector, apartial reflector positioned at a distance from the movable reflectorthereby forming an optical resonator cavity, an electrode configured tocause said movable minor to move with respect to said partial reflectorto alter said optical resonator cavity, and a substrate, said movablereflector, said partial reflector and said electrode disposed on oneside of a substrate, said substrate having a thickness of about 0.45millimeter or less.

Still another embodiment has a display comprising a plurality of displayelements, each of the display elements comprising a movable reflector, apartial reflector positioned at a distance from the movable reflectorthereby forming an optical resonator cavity, said movable reflector andsaid partial reflector separated by a gap, a diffuser portion disposedforward the movable and partial reflectors, and an electrode configuredto cause said movable reflector to move with respect to said partialreflector and to alter said optical resonator cavity, wherein saiddiffuser portion is disposed within about 0.45 millimeter of saidpartial reflector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of aninterferometric modulator display in which a movable reflective layer ofa first interferometric modulator is in a relaxed position and a movablereflective layer of a second interferometric modulator is in an actuatedposition.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device incorporating a 3×3 interferometric modulator display.

FIG. 3 is a diagram of movable minor position versus applied voltage forone exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that maybe used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row andcolumn signals that may be used to write a frame of display data to the3×3 interferometric modulator display of FIG. 2.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa visual display device comprising a plurality of interferometricmodulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of aninterferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of aninterferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of aninterferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of aninterferometric modulator.

FIG. 8 illustrates a cross-section of an embodiment of a display devicecomprising an interferometric optical modulator and a diffuser.

FIG. 9 illustrates a cross-section of an embodiment of a diffuser withan optical texture or optical features formed on a surface thereof.

FIG. 10 provides a flowchart of a method for manufacturing a displaydevice comprising an interferometric optical modulator and diffuser.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following detailed description is directed to certain specificembodiments of the invention. However, the invention can be embodied ina multitude of different ways. In this description, reference is made tothe drawings wherein like parts are designated with like numeralsthroughout. As will be apparent from the following description, theembodiments may be implemented in any device that is configured todisplay an image, whether in motion (e.g., video) or stationary (e.g.,still image), and whether textual or pictorial. More particularly, it iscontemplated that the embodiments may be implemented in or associatedwith a variety of electronic devices such as, but not limited to, mobiletelephones, wireless devices, personal data assistants (PDAs), hand-heldor portable computers, GPS receivers/navigators, cameras, MP3 players,camcorders, game consoles, wrist watches, clocks, calculators,television monitors, flat panel displays, computer monitors, autodisplays (e.g., odometer display, etc.), cockpit controls and/ordisplays, display of camera views (e.g., display of a rear view camerain a vehicle), electronic photographs, electronic billboards or signs,projectors, architectural structures, packaging, and aestheticstructures (e.g., display of images on a piece of jewelry). MEMS devicesof similar structure to those described herein can also be used innon-display applications such as in electronic switching devices.

Various embodiments of the invention include an interferometric opticalmodulator comprising a substrate layer having a thickness between about0.1 mm and about 0.5 mm thick. Such an interferometric modulator may beintegrated with a diffuser in a display device. The thin substratepermits the use of a thicker diffuser, while maintaining a substantiallyequal or thinner thickness of the display device. In some embodiments,the interferometric optical modulator comprises a substrate having afirst face and a second face, an optical stack fabricated on the firstface of the substrate, a mirror/mechanical assembly spaced from theoptical stack, and a diffuser applied to the second face of thesubstrate, wherein the substrate is less than about 0.5 mm thick. Thediffuser may be greater than about 0.1 mm thick in certain embodiments.

One interferometric modulator display embodiment comprising aninterferometric MEMS display element is illustrated in FIG. 1. In thesedevices, the pixels are in either a bright or dark state. In the bright(“on” or “open”) state, the display element reflects a large portion ofincident visible light to a user. When in the dark (“off” or “closed”)state, the display element reflects little incident visible light to theuser. Depending on the embodiment, the light reflectance properties ofthe “on” and “off” states may be reversed. MEMS pixels can be configuredto reflect predominantly at selected colors, allowing for a colordisplay in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series ofpixels of a visual display, wherein each pixel comprises a MEMSinterferometric modulator. In some embodiments, an interferometricmodulator display comprises a row/column array of these interferometricmodulators. Each interferometric modulator includes a pair of reflectivelayers positioned at a variable and controllable distance from eachother to form a resonant optical cavity with at least one variabledimension. In one embodiment, one of the reflective layers may be movedbetween two positions. In the first position, referred to herein as therelaxed position, the movable reflective layer is positioned at arelatively large distance from a fixed partially reflective layer. Inthe second position, referred to herein as the actuated position, themovable reflective layer is positioned more closely adjacent to thepartially reflective layer. Incident light that reflects from the twolayers interferes constructively or destructively depending on theposition of the movable reflective layer, producing either an overallreflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacentinterferometric modulators 12 a and 12 b. In the interferometricmodulator 12 a on the left, a movable reflective layer 14 a isillustrated in a relaxed position at a predetermined distance from anoptical stack 16 a, which includes a partially reflective layer. In theinterferometric modulator 12 b on the right, the movable reflectivelayer 14 b is illustrated in an actuated position adjacent to theoptical stack 16 b.

The optical stacks 16 a and 16 b (collectively referred to as opticalstack 16), as referenced herein, typically comprise of several fusedlayers, which can include an electrode layer, such as indium tin oxide(ITO), a partially reflective layer, such as chromium, and a transparentdielectric. The optical stack 16 is thus electrically conductive,partially transparent and partially reflective, and may be fabricated,for example, by depositing one or more of the above layers onto atransparent substrate 20. In some embodiments, the layers are patternedinto parallel strips, and may form row electrodes in a display device asdescribed further below. The movable reflective layers 14 a, 14 b may beformed as a series of parallel strips of a deposited metal layer orlayers (orthogonal to the row electrodes of 16 a, 16 b) deposited on topof posts 18 and an intervening sacrificial material deposited betweenthe posts 18. When the sacrificial material is etched away, the movablereflective layers 14 a, 14 b are separated from the optical stacks 16 a,16 b by a defined gap 19. A highly conductive and reflective materialsuch as aluminum may be used for the reflective layers 14, and thesestrips may form column electrodes in a display device.

With no applied voltage, the cavity 19 remains between the movablereflective layer 14 a and optical stack 16 a, with the movablereflective layer 14 a in a mechanically relaxed state, as illustrated bythe pixel 12 a in FIG. 1. However, when a potential difference isapplied to a selected row and column, the capacitor formed at theintersection of the row and column electrodes at the corresponding pixelbecomes charged, and electrostatic forces pull the electrodes together.If the voltage is high enough, the movable reflective layer 14 isdeformed and is forced against the optical stack 16. A dielectric layer(not illustrated in this Figure) within the optical stack 16 may preventshorting and control the separation distance between layers 14 and 16,as illustrated by pixel 12 b on the right in FIG. 1. The behavior is thesame regardless of the polarity of the applied potential difference. Inthis way, row/column actuation that can control the reflective vs.non-reflective pixel states is analogous in many ways to that used inconventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for usingan array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of anelectronic device that may incorporate aspects of the invention. In theexemplary embodiment, the electronic device includes a processor 21which may be any general purpose single- or multi-chip microprocessorsuch as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®,Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any specialpurpose microprocessor such as a digital signal processor,microcontroller, or a programmable gate array. As is conventional in theart, the processor 21 may be configured to execute one or more softwaremodules. In addition to executing an operating system, the processor maybe configured to execute one or more software applications, including aweb browser, a telephone application, an email program, or any othersoftware application.

In one embodiment, the processor 21 is also configured to communicatewith an array driver 22. In one embodiment, the array driver 22 includesa row driver circuit 24 and a column driver circuit 26 that providesignals to a panel or display array (display) 30. The cross section ofthe array illustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. ForMEMS interferometric modulators, the row/column actuation protocol maytake advantage of a hysteresis property of these devices illustrated inFIG. 3. It may require, for example, a 10 volt potential difference tocause a movable layer to deform from the relaxed state to the actuatedstate. However, when the voltage is reduced from that value, the movablelayer maintains its state as the voltage drops back below 10 volts. Inthe exemplary embodiment of FIG. 3, the movable layer does not relaxcompletely until the voltage drops below 2 volts. There is thus a rangeof voltage, about 3 to 7 V in the example illustrated in FIG. 3, wherethere exists a window of applied voltage within which the device isstable in either the relaxed or actuated state. This is referred toherein as the “hysteresis window” or “stability window.” For a displayarray having the hysteresis characteristics of FIG. 3, the row/columnactuation protocol can be designed such that during row strobing, pixelsin the strobed row that are to be actuated are exposed to a voltagedifference of about 10 volts, and pixels that are to be relaxed areexposed to a voltage difference of close to zero volts. After thestrobe, the pixels are exposed to a steady state voltage difference ofabout 5 volts such that they remain in whatever state the row strobe putthem in. After being written, each pixel sees a potential differencewithin the “stability window” of 3-7 volts in this example. This featuremakes the pixel design illustrated in FIG. 1 stable under the sameapplied voltage conditions in either an actuated or relaxed pre-existingstate. Since each pixel of the interferometric modulator, whether in theactuated or relaxed state, is essentially a capacitor formed by thefixed and moving reflective layers, this stable state can be held at avoltage within the hysteresis window with almost no power dissipation.Essentially no current flows into the pixel if the applied potential isfixed.

In typical applications, a display frame may be created by asserting theset of column electrodes in accordance with the desired set of actuatedpixels in the first row. A row pulse is then applied to the row 1electrode, actuating the pixels corresponding to the asserted columnlines. The asserted set of column electrodes is then changed tocorrespond to the desired set of actuated pixels in the second row. Apulse is then applied to the row 2 electrode, actuating the appropriatepixels in row 2 in accordance with the asserted column electrodes. Therow 1 pixels are unaffected by the row 2 pulse, and remain in the statethey were set to during the row 1 pulse. This may be repeated for theentire series of rows in a sequential fashion to produce the frame.Generally, the frames are refreshed and/or updated with new display databy continually repeating this process at some desired number of framesper second. A wide variety of protocols for driving row and columnelectrodes of pixel arrays to produce display frames are also well knownand may be used in conjunction with the present invention.

FIGS. 4 and 5 illustrate one possible actuation protocol for creating adisplay frame on the 3×3 array of FIG. 2. FIG. 4 illustrates a possibleset of column and row voltage levels that may be used for pixelsexhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment,actuating a pixel involves setting the appropriate column to −V_(bias),and the appropriate row to +ΔV, which may correspond to −5 volts and +5volts respectively Relaxing the pixel is accomplished by setting theappropriate column to +V_(bias), and the appropriate row to the same+ΔV, producing a zero volt potential difference across the pixel. Inthose rows where the row voltage is held at zero volts, the pixels arestable in whatever state they were originally in, regardless of whetherthe column is at +V_(bias), or −V_(bias). As is also illustrated in FIG.4, it will be appreciated that voltages of opposite polarity than thosedescribed above can be used, e.g., actuating a pixel can involve settingthe appropriate column to +V_(bias), and the appropriate row to −ΔV. Inthis embodiment, releasing the pixel is accomplished by setting theappropriate column to −V_(bias), and the appropriate row to the same−ΔV, producing a zero volt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signalsapplied to the 3×3 array of FIG. 2 which will result in the displayarrangement illustrated in FIG. 5A, where actuated pixels arenon-reflective. Prior to writing the frame illustrated in FIG. 5A, thepixels can be in any state, and in this example, all the rows are at 0volts, and all the columns are at +5 volts. With these applied voltages,all pixels are stable in their existing actuated or relaxed states.

In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) areactuated. To accomplish this, during a “line time” for row 1, columns 1and 2 are set to −5 volts, and column 3 is set to +5 volts. This doesnot change the state of any pixels, because all the pixels remain in the3-7 volt stability window. Row 1 is then strobed with a pulse that goesfrom 0, up to 5 volts, and back to zero. This actuates the (1,1) and(1,2) pixels and relaxes the (1,3) pixel. No other pixels in the arrayare affected. To set row 2 as desired, column 2 is set to −5 volts, andcolumns 1 and 3 are set to +5 volts. The same strobe applied to row 2will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again,no other pixels of the array are affected. Row 3 is similarly set bysetting columns 2 and 3 to −5 volts, and column 1 to +5 volts. The row 3strobe sets the row 3 pixels as shown in FIG. 5A. After writing theframe, the row potentials are zero, and the column potentials can remainat either +5 or −5 volts, and the display is then stable in thearrangement of FIG. 5A. It will be appreciated that the same procedurecan be employed for arrays of dozens or hundreds of rows and columns. Itwill also be appreciated that the timing, sequence, and levels ofvoltages used to perform row and column actuation can be varied widelywithin the general principles outlined above, and the above example isexemplary only, and any actuation voltage method can be used with thesystems and methods described herein.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment ofa display device 40. The display device 40 can be, for example, acellular or mobile telephone. However, the same components of displaydevice 40 or slight variations thereof are also illustrative of varioustypes of display devices such as televisions and portable media players.

The display device 40 includes a housing 41, a display 30, an antenna43, a speaker 45, an input device 48, and a microphone 46. The housing41 is generally formed from any of a variety of manufacturing processesas are well known to those of skill in the art, including injectionmolding, and vacuum forming. In addition, the housing 41 may be madefrom any of a variety of materials, including but not limited toplastic, metal, glass, rubber, and ceramic, or a combination thereof. Inone embodiment the housing 41 includes removable portions (not shown)that may be interchanged with other removable portions of differentcolor, or containing different logos, pictures, or symbols.

The display 30 of exemplary display device 40 may be any of a variety ofdisplays, including a bi-stable display, as described herein. In otherembodiments, the display 30 includes a flat-panel display, such asplasma, EL, OLED, STN LCD, or TFT LCD as described above, or anon-flat-panel display, such as a CRT or other tube device, as is wellknown to those of skill in the art. However, for purposes of describingthe present embodiment, the display 30 includes an interferometricmodulator display, as described herein.

The components of one embodiment of exemplary display device 40 areschematically illustrated in FIG. 6B. The illustrated exemplary displaydevice 40 includes a housing 41 and can include additional components atleast partially enclosed therein. For example, in one embodiment, theexemplary display device 40 includes a network interface 27 thatincludes an antenna 43 which is coupled to a transceiver 47. Thetransceiver 47 is connected to the processor 21, which is connected toconditioning hardware 52. The conditioning hardware 52 may be configuredto condition a signal (e.g. filter a signal). The conditioning hardware52 is connected to a speaker 45 and a microphone 46. The processor 21 isalso connected to an input device 48 and a driver controller 29. Thedriver controller 29 is coupled to a frame buffer 28 and to the arraydriver 22, which in turn is coupled to a display array 30. A powersupply 50 provides power to all components as required by the particularexemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47so that the exemplary display device 40 can communicate with one or moredevices over a network. In one embodiment the network interface 27 mayalso have some processing capabilities to relieve requirements of theprocessor 21. The antenna 43 is any antenna known to those of skill inthe art for transmitting and receiving signals. In one embodiment, theantenna transmits and receives RF signals according to the IEEE 802.11standard, including IEEE 802.11(a), (b), or (g). In another embodiment,the antenna transmits and receives RF signals according to the BLUETOOTHstandard. In the case of a cellular telephone, the antenna is designedto receive CDMA, GSM, AMPS or other known signals that are used tocommunicate within a wireless cell phone network. The transceiver 47pre-processes the signals received from the antenna 43 so that they maybe received by and further manipulated by the processor 21. Thetransceiver 47 also processes signals received from the processor 21 sothat they may be transmitted from the exemplary display device 40 viathe antenna 43.

In an alternative embodiment, the transceiver 47 can be replaced by areceiver. In yet another alternative embodiment, network interface 27can be replaced by an image source, which can store or generate imagedata to be sent to the processor 21. For example, the image source canbe a digital video disc (DVD) or a hard-disc drive that contains imagedata, or a software module that generates image data.

Processor 21 generally controls the overall operation of the exemplarydisplay device 40. The processor 21 receives data, such as compressedimage data from the network interface 27 or an image source, andprocesses the data into raw image data or into a format that is readilyprocessed into raw image data. The processor 21 then sends the processeddata to the driver controller 29 or to frame buffer 28 for storage. Rawdata typically refers to the information that identifies the imagecharacteristics at each location within an image. For example, suchimage characteristics can include color, saturation, and gray-scalelevel.

In one embodiment, the processor 21 includes a microcontroller, CPU, orlogic unit to control operation of the exemplary display device 40.Conditioning hardware 52 generally includes amplifiers and filters fortransmitting signals to the speaker 45, and for receiving signals fromthe microphone 46. Conditioning hardware 52 may be discrete componentswithin the exemplary display device 40, or may be incorporated withinthe processor 21 or other components.

The driver controller 29 takes the raw image data generated by theprocessor 21 either directly from the processor 21 or from the framebuffer 28 and reformats the raw image data appropriately for high speedtransmission to the array driver 22. Specifically, the driver controller29 reformats the raw image data into a data flow having a raster-likeformat, such that it has a time order suitable for scanning across thedisplay array 30. Then the driver controller 29 sends the formattedinformation to the array driver 22. Although a driver controller 29,such as a LCD controller, is often associated with the system processor21 as a stand-alone Integrated Circuit (IC), such controllers may beimplemented in many ways. They may be embedded in the processor 21 ashardware, embedded in the processor 21 as software, or fully integratedin hardware with the array driver 22.

Typically, the array driver 22 receives the formatted information fromthe driver controller 29 and reformats the video data into a parallelset of waveforms that are applied many times per second to the hundredsand sometimes thousands of leads coming from the display's x-y matrix ofpixels.

In one embodiment, the driver controller 29, array driver 22, anddisplay array 30 are appropriate for any of the types of displaysdescribed herein. For example, in one embodiment, driver controller 29is a conventional display controller or a bi-stable display controller(e.g., an interferometric modulator controller). In another embodiment,array driver 22 is a conventional driver or a bi-stable display driver(e.g., an interferometric modulator display). In one embodiment, adriver controller 29 is integrated with the array driver 22. Such anembodiment is common in highly integrated systems such as cellularphones, watches, and other small area displays. In yet anotherembodiment, display array 30 is a typical display array or a bi-stabledisplay array (e.g., a display including an array of interferometricmodulators).

The input device 48 allows a user to control the operation of theexemplary display device 40. In one embodiment, input device 48 includesa keypad, such as a QWERTY keyboard or a telephone keypad, a button, aswitch, a touch-sensitive screen, a pressure- or heat-sensitivemembrane. In one embodiment, the microphone 46 is an input device forthe exemplary display device 40. When the microphone 46 is used to inputdata to the device, voice commands may be provided by a user forcontrolling operations of the exemplary display device 40.

Power supply 50 can include a variety of energy storage devices as arewell known in the art. For example, in one embodiment, power supply 50is a rechargeable battery, such as a nickel-cadmium battery or a lithiumion battery. In another embodiment, power supply 50 is a renewableenergy source, a capacitor, or a solar cell, including a plastic solarcell, and solar-cell paint. In another embodiment, power supply 50 isconfigured to receive power from a wall outlet.

In some implementations control programmability resides, as describedabove, in a driver controller which can be located in several places inthe electronic display system. In some cases control programmabilityresides in the array driver 22. Those of skill in the art will recognizethat the above-described optimization may be implemented in any numberof hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operatein accordance with the principles set forth above may vary widely. Forexample, FIGS. 7A-7E illustrate five different embodiments of themovable reflective layer 14 and its supporting structures. FIG. 7A is across section of the embodiment of FIG. 1, where a strip of metalmaterial 14 is deposited on orthogonally extending supports 18. In FIG.7B, the moveable reflective layer 14 is attached to supports at thecorners only, on tethers 32. In FIG. 7C, the moveable reflective layer14 is suspended from a deformable layer 34, which may comprise aflexible metal. The deformable layer 34 connects, directly orindirectly, to the substrate 20 around the perimeter of the deformablelayer 34. These connections are herein referred to as support posts. Theembodiment illustrated in FIG. 7D has support post plugs 42 upon whichthe deformable layer 34 rests. The movable reflective layer 14 remainssuspended over the cavity, as in FIGS. 7A-7C, but the deformable layer34 does not form the support posts by filling holes between thedeformable layer 34 and the optical stack 16. Rather, the support postsare formed of a planarization material, which is used to form supportpost plugs 42. The embodiment illustrated in FIG. 7E is based on theembodiment shown in FIG. 7D, but may also be adapted to work with any ofthe embodiments illustrated in FIGS. 7A-7C as well as additionalembodiments not shown. In the embodiment shown in FIG. 7E, an extralayer of metal or other conductive material has been used to form a busstructure 44. This allows signal routing along the back of theinterferometric modulators, eliminating a number of electrodes that mayotherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 7, the interferometricmodulators function as direct-view devices, in which images are viewedfrom the front side of the transparent substrate 20, the side oppositeto that upon which the modulator is arranged. In these embodiments, thereflective layer 14 optically shields some portions of theinterferometric modulator on the side of the reflective layer oppositethe substrate 20, including the deformable layer 34 and the busstructure 44. This allows the shielded areas to be configured andoperated upon without negatively affecting the image quality. Thisseparable modulator architecture allows the structural design andmaterials used for the electromechanical aspects and the optical aspectsof the modulator to be selected and to function independently of eachother. Moreover, the embodiments shown in FIGS. 7C-7E have additionalbenefits deriving from the decoupling of the optical properties of thereflective layer 14 from its mechanical properties, which are carriedout by the deformable layer 34. This allows the structural design andmaterials used for the reflective layer 14 to be optimized with respectto the optical properties, and the structural design and materials usedfor the deformable layer 34 to be optimized with respect to desiredmechanical properties.

An advantage of interferometric modulator devices is that unlike otherdisplay technologies such as LCDs, a polarizer is not required. Becausethere is no polarizer, incident light of all polarizations can be used,rather than sacrificing half of the light to ensure known polarization.

Because the mirrors in interferometric modulator devices are specular, adiffuser may be used to modify the look of the display to be morediffuse, for example, more like paper. This diffuser may comprise adiffusing film. This diffusing film may be interposed between theinteferometric modulator and the viewer. The diffusing film can beapplied to the substrate of the interferometric optical modulator afterfabrication of this interferometric modulators. The diffuser maycomprise a polymer film, for example, polyester or polycarbonate, havinga thickness from about 50 μm to about 100 μm. Such films can be fragile,thereby reducing the yield of the devices because the optical defectsintroduced by improperly handled films. Such films also often do notprovide the desired level of diffusion. Furthermore, such films areoften difficult to manufacture, making them expensive and difficult toobtain. A thicker diffuser, however, will increase the overall thicknessof the device.

Accordingly, in certain embodiments a display device may be fabricatedthat comprises an interferometric modulator comprising a thintransparent substrate. This thin substrate permits the use of a thickerdiffuser while maintaining an acceptable stack height. Structures andmethods for fabricating interferometric optical modulators are known inthe art are described above as well as in, for example, in U.S. Pat. No.5,835,255, which is incorporated herein by reference in its entirety.U.S. application Ser. No. 10/941,042, titled “Method for fabricating aStructure for a Microelectromechanical System (MEMS) Device”, filed Sep.14, 2004, now U.S. Pat. No. 7,250,315, U.S. Provisional Application No.60/613,496, titled “Method of Fabricating Interferometric Devices usingLift-Off Processing Techniques”, filed Sep. 27, 2004, and U.S.Provisional Application No. 60/613,452, titled “Method of Making aReflective Display Device using thin Film Transistor ProductionTechniques”, filed Sep. 27, 2004, also describe structure and methodsfor fabricating interferometric modulators, and are incorporated hereinby reference in their entirety.

FIG. 8 is a cross-section of an exemplary display device 100 comprisingan interferometric modulator comprising a transparent substrate 102, anoptical stack 104, a mirror/mechanical assembly 106. The display devicefurther comprises a diffuser 108.

The movable mirror 106 may comprise a metal layer as described above. Asshown, the movable mirror is supported by posts 118. Other materials anddesigns are also possible. In some embodiments, the optical stack 104comprises a transparent conductor, a partially reflective material and adielectric as described above. Other configurations and designs are alsopossible.

The substrate 102 may comprise a transparent material such as, forexample, glass, plastic, silica, alumina, and the like. In someembodiments, the substrate 102 is glass. In some embodiments thesubstrate is less than about 0.5 mm thick, for example, up to about 0.45mm thick, or about 0.4 mm thick, or about 0.35 mm thick. In someembodiments the substrate is no more than about 0.3 mm thick, about 0.25mm thick, or about 0.2 mm thick. In other embodiments, the substrate hasa thickness of not greater than about 0.15 mm thick or about 0.1 mm. Insome embodiments other thicknesses are also used. A thinner substratealso allows for the diffuser to be positioned closer to theinterferometric cavity. Accordingly, the diffuser in some embodimentscan be closer than about 0.45 mm from the optical stack. In someembodiments, the diffuser is about 0.4, 0.35, or 0.3 mm from the opticalstack. In other embodiments, the diffuser is about 0.25, 0.2, 0.15, or0.1 mm from the optical stack. In other embodiments, the diffuser may becloser or farther from the optical stack.

An advantageous aspect of the closer proximity of the diffuser to thelight modulating elements (e.g. interferometric modulators) is anincrease in attainable contrast for higher resolution displays. Contrastis a characteristic of a display related to the difference betweenluminance of the brightest white and darkest black. A measure ofcontrast can be qualitatively determined by computing the ratio ofluminance between light and dark areas for a displayed test pattern. Thedisplayed pattern may comprise alternating white and black lines such asalternating bright and dark columns or rows. The columns or rows of sucha test pattern may each correspond to a single column or row of aninterferometric modulator array. The ratio of the maximum luminance ofthe bright line and to the minimum luminance of the dark line asmeasured at the output of the display (after the diffuser) is a measureof the contrast.

The spatial resolution of a display is dependent on the spatial periodof its elements, where spatial period is defined as the distance betweenlike portions of adjacent elements. For example, where the distance fromcenter to center, or left edge to left edge of adjacent rows of an arrayis a, the spatial period of the rows is a. The spatial resolution is,therefore, determined by the size and spacing of the individual lightmodulating elements, and is improved with the use of smaller elementswhich are positioned closer together.

If a diffuser is spaced apart from the light modulating elements by morethan about one period, a, the scattering of the light by the diffuserdetrimentally affects the contrast, and therefore, the viewer'sperception of the pattern or other images formed by the display. Withlarger distances separating the diffuser from the light modulatingelements, the light scattered by the diffuser deviates further from itsoriginal direction. As a result, instead of traveling directly to theviewer, light from a first light modulating element may be scattered bythe diffuser such that it appears to have come from a second adjacentlight modulating element. This deviation results in the redistributionof light and reduces the contrast observed by the viewer.

Consequently, maximum resolution for a desired contrast is limited bythe diffuser spacing from the modulating elements. Closer diffuserproximity to the light modulating elements allows for use of smallerlight modulating elements and smaller spatial periods to achieve higherresolution for a given desired contrast. For example, when the diffuseris placed about 0.45 mm from the interferometric modulator, a contrastof greater than about 5 to 1 may be attained while using a displayedtest pattern of alternating white and black lines having a spatialperiod of about 0.45 millimeter (mm) for a display that also has areflectivity at a viewing angle of about 45° that is at least about 75%of the reflectivity when viewed from normal. Similarly, when thediffuser is placed closer than about 0.3 mm, 0.2 mm, or 0.1 mm from theinterferometric modulator, similar or better contrast and reflectivityperformance under the same test conditions can be achieved for displayswith arrays of light modulating elements having pitches of about 0.3 mm,0.2 mm, or 0.1 mm, respectively. Other values outside these ranges,however, are also possible.

In some embodiments, the diffuser 108 comprises a suitable transparentor translucent polymer resin, for example, polyester, polycarbonate,polyvinyl chloride (PVC), polyvinylidene chloride, polystyrene,polyacrylates, polyethylene terephthalate, polyurethane, and copolymersor blends thereof. In other embodiments other materials are used. Insome embodiments, the diffuser 108 is a composite comprising a polymerresin as described above and one or more other components. In someembodiments, the other component is inorganic. In other embodiments, theother component is organic. In some embodiments, the other componentprovides diffusion to the diffuser 108. For example, in someembodiments, optical beads are dispersed within the diffuser. In otherembodiments, the diffuser 108 comprises a film coated with micron-sizedoptical beads. In some embodiments, the diffuser 108 is monolithic. Thematerial from which the diffuser 108 is manufactured may be inherentlydiffusive. In some embodiments, a surface of the diffuser 108 ispatterned to provide diffusion. Either the surface of the diffuser 108proximal to the viewer, the surface distal to the viewer, or both arepatterned. The diffusive patterns may comprise a random surface profile.Some embodiments use a combination of these diffusion mechanisms, forexample, texturing a surface of an inherently diffusive material.

In some embodiments, the diffuser 108 is an inorganic material. In someembodiments, the inorganic material comprises an oxide and/or nitride,for example, silica or alumina. In some embodiments, the inorganicmaterial is crystalline. In other embodiments, the inorganic material isamorphous. In other embodiments other materials are used.

In some embodiments the substrate 102 is thinner than the substrate usedin typical interferometric modulator devices, which permits using athicker diffuser 108, while maintaining a comparable or even thinnerstack height for the device. In some embodiments, the diffuser 108 is atleast about 0.1 mm, at least about 0.2 mm, or at least about 0.3 mm. Inother embodiments the diffuser 108 is at least about 0.4 mm or at leastabout 0.5 mm. In some embodiments other thicknesses are also used.Advantages of using a thicker diffuser 108 may include any one of thefollowing: more effective diffusion of light, lighter weight as thediffuser may comprise a lighter material than the substrate, and lowercost as the cost of a thick substrate may be higher than the cost of athick diffuser. Additionally, in some embodiments, the diffuser 108 ismore physically robust than a thinner diffuser, which improves yields.Also, in certain embodiments, the thicker diffuser 108 provides a moredurable overall device 100. In some embodiments, a thicker diffuser 108is more easily applied to the substrate 102 than a thinner diffuser,thereby improving throughput and/or reducing costs.

A further advantage of a thicker diffuser 108 is that the additionalthickness permits one to incorporate additional functionality, forexample, additional coatings. Examples include, but are not limited toantireflection, antiglare, and/or anti-scratch coatings of any typeknown in the art. In other embodiments, these additional functions areincorporated in the diffuse properties of the diffuser 108. In someembodiments, for example, the diffuser compensates for color shift as afunction of view angle, for example, as disclosed in U.S. applicationSer. No. 11/040,824, titled “METHOD AND DEVICE FOR COMPENSATING FORCOLOR SHIFT AS A FUNCTION OF ANGLE OF VIEW,” filed Jan. 21, 2005,published as U.S. Patent Publication No. 2006/0077522, now U.S. Pat. No.7,630,123, of which the disclosure is incorporated herein by referencein its entirety. As described above, thicker diffusers permit morediffusion. The thicker diffuser provides more optical path lengththrough which to operate on the light propagating therethrough.

In some embodiments the surface of the diffuser 108 proximal to theviewer, the surface distal to the viewer, or both are patterned toprovide additional functionality, for example, to provide a lens and/orto control view angle. In the embodiment illustrated in FIG. 9, anoptical texture or surface features is provided on the surface of thediffuser 108′ proximal to the viewer. The optical texture is provided byany means known in the art, for example, embossing, etching, and thelike. In the illustrated embodiment, the embossing forms lenses 110.This lens may be configured, for example, to collimate ambient lightbefore it enters the interferometric modulator, thereby reducing a colorshift effect that occurs at steep viewing angles. The optical texturemay provide at least one of a holographic lens, a diffractive lens, anda Fresnel lens.

Also provided is a method for fabricating a display device 100comprising an interferometric modulator and a diffuser 108. FIG. 10 is aflowchart illustrating an embodiment 300 of the method with reference tothe device 100 illustrated in FIG. 8. In step 302, an interferometricmodulator is fabricated on a substrate 102 using any method, forexample, as described above or, for example, in U.S. Pat. No. 5,835,255,which is incorporated herein by reference in its entirety. U.S.application Ser. No. 10/941,042, titled “Method for fabricating aStructure for a Microelectromechanical System (MEMS) Device”, filed Sep.14, 2004, now U.S. Pat. No. 7,250,315, U.S. Provisional Application No.60/613,496, titled “Method of Fabricating Interferometric Devices usingLift-Off Processing Techniques”, filed Sep. 27, 2004, and U.S.Provisional Application No. 60/613,452, titled “Method of Making aReflective Display Device using thin Film Transistor ProductionTechniques”, filed Sep. 27, 2004, also describe structure and methodsfor fabricating interferometric modulators, and are incorporated hereinby reference in their entirety.

In step 304, a diffuser 108 is then applied to the substrate 102. Insome embodiments, the diffuser 108 is applied using an adhesive. In someembodiments, the adhesive is pre-applied to the diffuser 108. In otherembodiments, the adhesive is applied to the substrate 102 after thefabrication of the interferometric modulator. Some embodiments use atwo-part adhesive in which a first component is applied to the diffuser108 and a second component is applied to the substrate 102. In someembodiments, the adhesive is pressure sensitive. In some embodiments,the adhesive is thermosetting. In other embodiments, the adhesive curesat about ambient temperature. In other embodiments, the adhesive isradiation-cured.

In some embodiments, the diffuser 108 is fabricated on the substrate102. For example, in some embodiments, an uncured polymer resin isapplied to the substrate 102 by means known in the art, for example, byspin coating, or calendaring. The polymer resin is then cured to formthe diffuser 108.

Optional step 306 provides one or more additional processing steps. Insome embodiments, an additional step is the application of additionallayers or coatings to the diffuser 108, for example, an antireflective,antiglare, and/or anti-scratch coating as described above. In otherembodiments, such coatings are pre-applied to or manufactured with thediffuser 108 and are applied simultaneously with the diffuser 108 instep 304. Another type of additional processing step modifies thesurface of the diffuser 108 proximal to the viewer, for example, bypolishing or roughening the surface, either chemically and/orphysically. In another embodiment, an additional processing stepprovides an optical texture or surface features described above, forexample, by embossing or engraving. In other embodiments, an opticaltexture or surface features are provided on the diffuser 108 prior tothe application of the diffuser in step 304.

Variations in the process for forming the device 100 are possible. Forexample, additional steps may be included, steps may be removed, and theorder of the steps may be altered. Similarly, the device may beconfigured differently. Additional components may be added, componentsmay be removed or the order and placement of the components may bealtered. The components may have different sizes, shaped, and featuresincorporated therein. The components may also comprise differentmaterials. In certain embodiments each of the interferometric modulatorsin an array includes a separate diffuser. In other embodiments, a singlediffuser is disposed forward a plurality of interferometric modulators,portions of the same diffuser overlapping individual interferometricmodulators. Still other variations are possible in the arrangement ofthe component elements and the configuration as well as use andapplication of the device.

Accordingly, while the above detailed description has shown, described,and pointed out novel features as applied to various embodiments, itwill be understood that various omissions, substitutions, and changes inthe form and details of the device or process illustrated may be made bythose skilled in the art without departing from the spirit of theinvention. As will be recognized, the present invention may be embodiedwithin a form that does not provide all of the features and benefits setforth herein, as some features may be used or practiced separately fromothers.

1. A display comprising: a substrate having a first side and a secondside; and a plurality of interferometric light modulators disposed overthe first side of the substrate, the plurality of interferometric lightmodulators having a pitch, each of the plurality of interferometriclight modulators configured to be individually actuated to modulatelight in response to an electrical signal, each of the interferometriclight modulators including a resonant optical cavity, wherein thesubstrate has a thickness between the first side and the second sidethat is less than approximately the pitch of the plurality ofinterferometric light modulators.
 2. The display of claim 1, wherein atleast some of the plurality of interferometric light modulators include:a partial reflector; and a movable reflector spaced from the partialreflector by a gap, the movable reflector configured to move withrespect to the partial reflector to alter the gap to interferometricallymodulate light, the movable reflector configured to move in response toan electrical signal.
 3. The display of claim 2, further including anelectrode configured to cause the movable reflector to move with respectto the partial reflector in response to the electrical signal, theelectrode disposed on the same side of the gap as the partial reflector.4. The display of claim 1, wherein the display is configured as areflective display.
 5. The display of claim 1, wherein the pitch of theplurality of interferometric light modulators is less than about 0.45mm.
 6. The display of claim 1, wherein the pitch of the plurality ofinterferometric light modulators is less than about 0.3 mm.
 7. Thedisplay of claim 1, wherein the pitch of the plurality ofinterferometric light modulators is less than about 0.2 mm.
 8. Thedisplay of claim 1, wherein the pitch of the plurality ofinterferometric light modulators is less than about 0.1 mm.
 9. Thedisplay of claim 1, further including a diffuser.
 10. The display ofclaim 9, wherein the diffuser is disposed over the second side of thesubstrate.
 11. The display of claim 10, wherein the display isconfigured such that the first side of the substrate is distal to aviewer of the display and the second side of the substrate is proximalto the viewer.
 12. The display of claim 9, wherein the display isconfigured such that light incident on the display passes through thediffuser before being incident on the plurality of interferometric lightmodulators.
 13. The display of claim 9, wherein the diffuser is disposedover the first side of the substrate, and the plurality ofinterferometric light modulators are disposed over the diffuser.
 14. Thedisplay of claim 9, wherein the diffuser has a thickness of less thanabout 0.4 mm.
 15. The display of claim 9, wherein the diffuser includesa material having a lower density than the substrate.
 16. The display ofclaim 9, wherein the diffuser is a composite including two or morecomponents, wherein at least one of the two or more components providesdiffusion to the diffuser.
 17. The display of claim 1, furthercomprising: a processor configured to process image data; and a memorydevice in electrical communication with the processor.
 18. The displayof claim 17, further including a driver circuit configured to send atleast one signal to the display.
 19. The display of claim 18, furtherincluding a controller configured to send at least a portion of theimage data to the driver circuit.
 20. The display of claim 17, furtherincluding an image source module configured to send the image data tothe processor.
 21. The display of claim 20, wherein the image sourcemodule includes at least one of a receiver, transceiver, andtransmitter.
 22. The display of claim 17, further including an inputdevice configured to receive input data and to communicate the inputdata to the processor.
 23. A display comprising: a substrate having afirst side and a second side; and a plurality of means forinterferometrically modulating light, the plurality ofinterferometrically modulating light means disposed over the first sideof the substrate, the plurality of interferometrically modulating lightmeans having a pitch, each of the plurality of interferometricallymodulating light means configured to be individually actuated tomodulate light in response to an electrical signal, each of theinterferometrically modulating light means including a resonant opticalcavity, wherein the substrate has a thickness between the first side andthe second side that is less than approximately the pitch of theplurality of interferometrically modulating light means.
 24. The displayof claim 23, wherein the interferometrically modulating light meansincludes an interferometric light modulator.
 25. The display of claim23, wherein the interferometrically modulating light means includes: apartial reflector; and a movable reflector spaced from the partialreflector by a gap, the movable reflector configured to move withrespect to the partial reflector to alter the gap to interferometricallymodulate light, the movable reflector configured to move in response toan electrical signal.
 26. The display of claim 25, further including anelectrode configured to cause the movable reflector to move with respectto the partial reflector in response to the electrical signal, theelectrode disposed on the same side of the gap as the partial reflector.27. The display of claim 23, wherein the display is configured as areflective display.
 28. The display of claim 23, wherein the pitch ofthe plurality of interferometrically modulating light means is less thanabout 0.45 mm.
 29. The display of claim 23, further including means fordiffusing light.
 30. The display of claim 29, wherein the diffusingmeans includes a diffuser.
 31. The display of claim 29, wherein themeans for diffusing light is disposed over the second side of thesubstrate.
 32. The display of claim 29, wherein the means for diffusinglight is disposed over the first side of the substrate and the pluralityof interferometrically modulating light means are disposed over thediffuser.
 33. A method of manufacturing a display, the display includinga plurality of display elements having a spatial pitch, the methodcomprising, for each display element: forming a movable reflector;forming a partial reflector positioned at a distance from the movablereflector thereby forming an optical resonator cavity; and forming anelectrode configured to cause the movable reflector to move with respectto the partial reflector to alter the optical resonator cavity; whereinthe movable reflector, the partial reflector and the electrode aredisposed over one side of a substrate, the substrate having a thicknessof less than approximately the spatial pitch of the plurality of displayelements.
 34. The method of claim 33, wherein the spatial pitch of theplurality of display elements is approximately 0.45 millimeters or less.35. The method of claim 33, further including providing a diffuserspaced apart from the partial reflector.
 36. The method of claim 35,wherein the substrate has a first side and a second side, and themovable reflector, the partial reflector and the electrode are disposedover the first side of the substrate, the method including disposing thediffuser over the second side of the substrate.
 37. The method of claim35, wherein the substrate has a first side and a second side, the methodincluding disposing the diffuser over the first side of the substrateand disposing the movable reflector, the partial reflector and theelectrode over the diffuser.